Development of new persistent luminescent composites using modified direct doping method

Abstract

The principal aim of this thesis was to create novel persistent luminescent composites that display green persistent luminescence (PeL) when charged not only with UV light but also with infrared radiation. The fundamental formula of the oxyfluorophosphate glasses was developed based on previous research undertaken at Tampere University's Photonics Glasses Group. The study's novelty was the use of a new host crystal from the tungstate calcium family (CaWO₄) codoped with Ytterbium and Thulium, able to absorb infrared radiation as well as emit visible light. The project was divided into three different phases. The first phase was dedicated to the investigation and improvement of blue upconversion (UC) in crystals after 980 nm irradiation. Using solid-state reaction, crystals with various Yb³⁺/Tm³⁺ ratios were produced and analyzed using SEM/EDS and XRD analyses. In addition, the blue upconversion following infrared stimulation was studied using different codoping ratios. The second step was intended to create composites by adding the most promising upconverter crystal and phosphors with green persistent luminescence in the glass. After infrared charging, green afterglow was seen, demonstrating the transfer of energy between Yb³⁺ ion and Tm³⁺ ions and then to persistent luminescence particles, implying that newly formed composites might be utilized to construct an optical battery. The third phase included adding silver to the most promising upconverter composite in order to gain superior blue emission.